Urine drug screens: When might a test result be false-positive?

Clinical recommendations
When a POC drug screen is positive, con­firming the result with GC–MS is good clinical practice. False positives can strain the relationship between patient and pro­vider, thus compromising care. Examining the procedures that were used to obtain the specimen, as well as double-checking POC test results, is, when appropriate, good medicine.

CASE CONTINUED
Because Mr. L is adamant about his sobriety and the fact that his drugs of choice were sedatives, not stimulants, the clinician orders a second drug screen by GC–MS. The second screen is negative for substances of abuse; Mr. L’s clinician concludes that bupropion pro­duced a false-positive result on the POC urine drug screen, confirming Mr. L’s assertions.

Related Resources
• Saitman A, Park HD, Fitzgerald RL. False-positive interferences of common urine drug screen immunoas­says: a review. J Anal Toxicol. 2014;38(7):387-396.
• Tenore PL. Advanced urine toxicology testing. J Addict Dis. 2010;29(4):436-448.

Drug Brand Names
Amantadine • Symadine, Symmetrel
Amitriptyline • Elavil
Atorvastatin • Lipitor
Brompheniramine • Dimetane
Bupropion • Wellbutrin, Zyban
Carbamazepine • Carbatrol, Tegretol
Chlorpromazine • Thorazine
Clomipramine • Anafranil
Cyclobenzaprine • Amrix, Flexeril
Cyproheptadine • Periactin
Desipramine • Nopramin
Desoxyephedrine • Desoxyn
Dextromethorphan • Delsym, Robitussin
Dicyclomine • Bentyl, Dicyclocot
Diphenhydramine • Benadryl, Unisom
Doxylamine • Robitussin, NyQuil
Dronabinol • Marinol
Efavirenz • Sustiva
Ephedrine • Mistol, Va-Tro-Nol
Ergotamine • Ergomar, Cafergot
Hydrocodone • Vicodin
Hydromophone • Dilaudid, Palladone
Hydroxyzine • Atarax, Vistaril
Isometheptene • Amidrine, Migrend
Isoxsuprine • Vasodilan, Vasoprine
Ketoprofen • Orudis, Oruvail
Labetalol • Normodyne, Trandate
Lisinopril • Prinivil, Zestril
Meperidine • Demerol
Naproxen • Aleve, Naprosyn
Oxaprozin • Daypro
Oxycodone • Oxycontin, Percocet, Percodan, Roxicodone
Phentermine • Adipex, Phentrol
Phenylephrine • Sudafed PE, Neo-Synephrine
Piroxicam • Feldene
Promethazine • Phenergan
Pseudoephedrine • Sudafed, Dimetapp
Quetiapine • Seroquel
Ranitidine • Zantac
Rifampin • Rifadin, Rimactane
Selegiline • EMSAM
Sertraline • Zoloft
Sulindac • Clinoril
Sumatriptan • Imitrex
Thioridazine • Mellaril
Tolmetin • Tolectin
Trazodone • Desyrel, Oleptro
Trimethobenzamide • Benzacot, Tigan
Trimipramine • Surmontil
Verapamil • Calan, Isoptin